Thousands of pounds of cash was handed to buyer John Maylam, who splashed out on lavish meals and stays at top London hotels, Croydon Crown Court heard.

Behagg, of Chatteris, was convicted of one charge of corruption.

Judge Nicholas Ainley warned him: “For any case of this magnitude a sentence of imprisonment is almost inevitably passed, and a significant one at that.”

Behagg is expected to be sentenced on 22 June at the same court alongside Maylam, 44, of Bearstead in Maidstone, Kent, and Greenvale’s account manager David Baxter, 50, of Hinstock, Market Drayton, Shropshire, who have both admitted corruption.

Employee’s suspicions

The prosecution’s case was that Sainsbury’s was overcharged by a total of £3.8m by Greenvale.

The extra money went into an account, then some of it was channelled to the buyer.

Maylam would incur expenses of £20,000 a month, spending the cash on expensive restaurants and exclusive hotels including Claridge’s and The Dorchester, the court heard.

The crime was uncovered when a Greenvale employee grew suspicious when he was asked to withdraw £5,000 bundles of £50 notes from a small local bank.

Jurors heard Simon Forster, a group financial accountant, found payments were being entered into their financial system as “entertaining” expenses and then written off as “raw materials” or storage costs for potatoes at fictitious firms in Spain and the UK.

Mr Forster said when he raised the payments with Behagg he was told they were “rebates” and part of a “scheme”.

‘Abuse’

Behagg told the court Greenvale had a two-year contract, worth £40m, to supply 45% of Sainsbury’s UK potatoes at the time of the alleged corruption.

Describing the size of Greenvale, Behagg said it handles 10% of the UK potato crop, amounting to 600,000 tonnes a year.

Following the verdict, Produce Investments, the owners of Greenvale, said it had introduced new procedures to “make sure that such abuse can never happen again”.

“Our relationship with Sainsbury’s is now on a footing as before and we continue to be one of the largest suppliers of potatoes to shoppers all over the country.”